1. Field of the Invention
The present invention relates to a method for recording information on the control track of a storage medium, in particular additional information on the control track (CTL track) of a video tape of the kind used in a video recorder.
2. Description of the Prior Art
Video tapes, such as those according to the VHS standard, for example, contain at least one control or CTL track on which control and trigger information items, which are used by the machine for corresponding control purposes, are written. In order to be able to use the CTL track for writing other information items as well, a CTL coding method is defined wherein a logic zero xe2x80x9c0xe2x80x9d and a logic one xe2x80x9c1xe2x80x9d are defined by way of the change in the duty ratio of the recorded control pulses, in that a mark-space ratio of 60:40 is stipulated for logic zero xe2x80x9c0xe2x80x9d and one of 27.5:72.5 is stipulated for logic one xe2x80x9c1xe2x80x9d. By means of this definition, a so-called VISS (Video Index Search System) and VASS (Video Address Search System) data format is stipulated, on the one hand the VISS data format having the following composition: one bit zero xe2x80x9c0xe2x80x9d, followed by 61xc2x13 bits one xe2x80x9c1xe2x80x9d, and subsequently one bit zero xe2x80x9c0xe2x80x9d, and on the other hand the VASS data format comprising 4 headers and three BCD data blocks. In this case, a BCD data block is 4 bits long and a header comprises 1 bit zero xe2x80x9c0xe2x80x9d, followed by 9 bits xe2x80x9c1xe2x80x9d and a subsequent bit zero xe2x80x9c0xe2x80x9d. In both data formats, the first bit zero xe2x80x9c0xe2x80x9d viewed in the writing direction forms the reference position. VISS is used according to the above definition as position marking (Index) and VASS as address recording. Furthermore, the 16:9 format can additionally be written onto the CTL track as video information.
A disadvantage of the above known methods is their limited usability, that is to say it is thus not possible to record additional information items such as tape counts, film titles or the like on the CTL track.
The object of the present invention, therefore, is to develop a method which can be used to record additional information items on the CTL track.
This object is achieved by means of the method according to claim 1. The subclaims relate to advantageous refinements of the invention.
In the method for writing information onto the control track of a storage medium for a tape recording machine, in particular of a video recorder, it is preferable that the data X to be recorded be converted into a code Y of a type such that it permits unambiguous detection of the data within the control track of the storage medium. In general, the control track of the storage medium, which is normally realized by a magnetic tape, is occupied by the information item xe2x80x9c0xe2x80x9d during recording.
In a first embodiment of the method according to the invention, the conversion of the data X into the data Y is carried out according to the following rules:
a) limitation of the number of successive logic zeros xe2x80x9c0xe2x80x9d and logic ones xe2x80x9c1xe2x80x9d to a maximum value max, where
b) the maximum value max must be smaller than that of any possible combination of successive zeros xe2x80x9c0xe2x80x9d or ones xe2x80x9c1xe2x80x9d used in other standards which are used for marking the control track,
c) arrangement of a header for switching on and of a header for switching off the data detection before and after the coded data.
In this case, the headers are formed according to the as following rules:
d) the header for switching on the data detection comprises a number N of logic zeros xe2x80x9c0xe2x80x9d, where min N=max+1, followed by a logic one xe2x80x9c1xe2x80x9d or any typical data pattern,
e) the header for switching off the data detection comprises N successive logic zeros xe2x80x9c0xe2x80x9d or any typical data pattern or a defined number of bits of the data stream.
In order to simplify the coding, or to avoid superfluous redundancy, the logic one xe2x80x9c1xe2x80x9d or the typical data pattern of the header for switching on the data reading is already a component part of the coding of the first data block, or rather the data block adjoining the header. In other words, the data blocks of the coded data always begin with a logic one xe2x80x9c1xe2x80x9d in this case. In this embodiment, a coded data block has a fixed length Zxe2x89xa7N.
The maximum value max of successive logic zeros xe2x80x9c0xe2x80x9d or ones xe2x80x9c1xe2x80x9d is preferably set to the value 3.
In a second embodiment of the method according to the invention, the data of the method according to the invention can comprise at least one coded data block, an unambiguously detectable header being transmitted before and after the at least one data block, and, in the case of a plurality of data blocks, the latter being separated by a header. In other words, n data blocks, where n is a natural number greater than zero, require n+1 headers. In this coding option, the information to be coded is coded by the length of the data block between the corresponding headers. Length is in this case generally understood to mean the number of bits in the above CTL coding method which are arranged between the headers, that is to say not the time elapsed between the corresponding headers, since the time is a function of the tape speed and would therefore not be an unambiguous measure for coding information items.
In consideration of the CTL method, a data block is preferably formed by a corresponding number of logic zeros xe2x80x9c0xe2x80x9d where, as already noted above, the information is encoded in the number of bits, that is to say number of logic zeros xe2x80x9c0xe2x80x9d.
The header in accordance with the method according to the invention comprises a typical bit pattern with a number of logic ones xe2x80x9c1xe2x80x9d, the number of logic ones xe2x80x9c1xe2x80x9d being less than or equal to the number of header bits. The header preferably comprises two logic ones xe2x80x9c1xe2x80x9d, that is to say the pattern xe2x80x9c11xe2x80x9d. Other patterns are possible.
A third embodiment of the method according to the invention, which is suitable for correcting the tape counter, writes a trigger information item onto the CTL track at predetermined time intervals, it being possible for the trigger information item to have different patterns, that is to say, in general, number of bits, which advantageously achieves a varying meaning of the different trigger information items. It is preferable for one logic one xe2x80x9c1xe2x80x9d or two logic ones xe2x80x9c1xe2x80x9d to be written alternately as trigger signal in each case at the end of the predetermined time interval. In this case, in one embodiment it is advantageous that the logic one xe2x80x9c1xe2x80x9d is written in each case for an even number of time intervals, while the pattern of two logic ones xe2x80x9c11xe2x80x9d is written for an odd number of time intervals. A suitable time interval selected for the application in a video recorder is one second, which is normally sufficient. Other interval lengths are possible and depend on the corresponding requirements. Thus, for example, a longer predetermined time interval is selected if the error of the tape counter is high.